Fix #115

Adds when_held event hook to Button (via extension of the EventsMixin
class). Also fixes some minor notes and activates codecov coverage
tracking.

docs/api_exc.rst

@@ -43,6 +43,10 @@ Errors
 
 .. autoexception:: BadEventHandler
 
+.. autoexception:: BadQueueLen
+
+.. autoexception:: BadWaitTime
+
 .. autoexception:: CompositeDeviceError
 
 .. autoexception:: CompositeDeviceBadName
@@ -63,10 +67,6 @@ Errors
 
 .. autoexception:: GPIOPinMissing
 
-.. autoexception:: GPIOBadQueueLen
-
-.. autoexception:: GPIOBadSampleWait
-
 .. autoexception:: InputDeviceError
 
 .. autoexception:: OutputDeviceError

docs/api_generic.rst

@@ -37,6 +37,9 @@ There are also several `mixin classes`_:
 * :class:`EventsMixin` which adds activated/deactivated events to devices
   along with the machinery to trigger those events
 
+* :class:`HoldMixin` which derives from :class:`EventsMixin` and adds the
+  held event to devices along with the machinery to repeatedly trigger it
+
 .. _mixin classes: https://en.wikipedia.org/wiki/Mixin
 
 The current class hierarchies are displayed below. For brevity, the mixin
@@ -141,3 +144,6 @@ Mixin Classes
 .. autoclass:: EventsMixin(...)
     :members:
 
+.. autoclass:: HoldMixin(...)
+    :members:
+

docs/api_pins.rst

@@ -72,7 +72,7 @@ to utilize pins that are part of IO extender chips. For example::
 
 .. warning::
 
-    The astute and mischievious reader may note that it is possible to mix pin
+    The astute and mischievous reader may note that it is possible to mix pin
     implementations, e.g. using ``RPiGPIOPin`` for one pin, and ``NativePin``
     for another. This is unsupported, and if it results in your script
     crashing, your components failing, or your Raspberry Pi turning into an